What is an earthquake?
Earthquakes are the shaking, rolling or sudden shock of the earth’s surface. Earthquakes happen along "fault lines" in the earth’s crust. Earthquakes can be felt over large areas although they usually last less than one minute.
They occur along all plate boundaries but are more destructive usually at destructive plate boundaries. Earthquakes cannot be predicted -- although scientists are working on it!
Why do earthquakes occur?
Most earthquakes occur when there is a movement along the plate boundaries and over 90% of all earthquakes take place at boundaries where there are converging plates.
At a plate boundary the plates move as a result of the convection currents but any movement is not steady or smooth. At times the plates become stuck just like teeth in a zip.
As the pressure builds up one plate will jerk past the other creating a sudden movement or earthquake. The point where the earthquake originates is called the focus and the area of land surface directly above it, the epicentre.
Earthquake measurements
The intensity of an earthquake can be measured. One measurement is called the Richter scale. Earthquakes below 4.0 on the Richter scale usually do not cause damage, and earthquakes below 2.0 usually can’t be felt.
Earthquakes over 5.0 on the scale can cause damage. A magnitude 6.0 earthquake is considered strong and a magnitude 7.0 is a major earthquake.
An earthquake causes both primary and secondary effects
Primary effects (the immediate damage)
Collapsing bridges and buildings
Cracked and twisted roads & other transport links
Death and injuries to individuals
Panic and shock of the people affected
Secondary effects (the after affects of an earthquake)
Fires caused by broken gas mains and electrical cables. Fires develop due to the lack of water from broken pipes
Tidal waves or Tsunamis often result from an earthquake such as the boxing day Tsunami in 2004.
Landslides in steep sided valleys where the rocks are often weak
Disease and famine due to lack of clean water and medical facilities
Death caused by the cold of winter such as in the Kashmir quake of 2005
Economic impacts - ie Many tourists were put off from visiting areas that had suffered due to the Boxing Day Tsunami
Major earthaquakes around the world:
A list of deadly quakes:
-Sept. 30, 2009: Indonesia, Sumatra, magnitude 7.9; more than 1000 dead and thousands missing.
-Oct. 7, 2005: Pakistan, India and Afghanistan, magnitude 7.6; more than 18,000 killed.
-Dec. 26, 2004: Indian Ocean, magnitude 9; more than 174,000 people killed, another 106,000 missing.
-Dec. 26, 2003: Southeastern Iran, Bam, magnitude 6.5; more than 26,000 killed.
-May 21, 2003: Northern Algeria, magnitude 6.8; nearly 2,300 killed.
-March 25, 2002: Northern Afghanistan, magnitude 5.8; up to 1,000 killed.
What is an earthquake?
Earthquakes are the shaking, rolling or sudden shock of the earth’s surface. Earthquakes happen along "fault lines" in the earth’s crust. Earthquakes can be felt over large areas although they usually last less than one minute.
They occur along all plate boundaries but are more destructive usually at destructive plate boundaries. Earthquakes cannot be predicted -- although scientists are working on it!
Why do earthquakes occur?
Most earthquakes occur when there is a movement along the plate boundaries and over 90% of all earthquakes take place at boundaries where there are converging plates.
At a plate boundary the plates move as a result of the convection currents but any movement is not steady or smooth. At times the plates become stuck just like teeth in a zip.
As the pressure builds up one plate will jerk past the other creating a sudden movement or earthquake. The point where the earthquake originates is called the focus and the area of land surface directly above it, the epicentre.
Earthquake measurements
The intensity of an earthquake can be measured. One measurement is called the Richter scale. Earthquakes below 4.0 on the Richter scale usually do not cause damage, and earthquakes below 2.0 usually can’t be felt.
Earthquakes over 5.0 on the scale can cause damage. A magnitude 6.0 earthquake is considered strong and a magnitude 7.0 is a major earthquake.
Simple Earthquake simulation
Instruments to measure earthquake
(a) Seismograph
(b)Seismometer
The effects of Earthquakes
An earthquake causes both primary and secondary effects
Primary effects (the immediate damage)
Secondary effects (the after affects of an earthquake)
- Fires caused by broken gas mains and electrical cables. Fires develop due to the lack of water from broken pipes
- Tidal waves or Tsunamis often result from an earthquake such as the boxing day Tsunami in 2004.
- Landslides in steep sided valleys where the rocks are often weak
- Disease and famine due to lack of clean water and medical facilities
- Death caused by the cold of winter such as in the Kashmir quake of 2005
- Economic impacts - ie Many tourists were put off from visiting areas that had suffered due to the Boxing Day Tsunami
Major earthaquakes around the world:A list of deadly quakes:
-Sept. 30, 2009: Indonesia, Sumatra, magnitude 7.9; more than 1000 dead and thousands missing.
-Oct. 7, 2005: Pakistan, India and Afghanistan, magnitude 7.6; more than 18,000 killed.
-Dec. 26, 2004: Indian Ocean, magnitude 9; more than 174,000 people killed, another 106,000 missing.
-Dec. 26, 2003: Southeastern Iran, Bam, magnitude 6.5; more than 26,000 killed.
-May 21, 2003: Northern Algeria, magnitude 6.8; nearly 2,300 killed.
-March 25, 2002: Northern Afghanistan, magnitude 5.8; up to 1,000 killed.
Further links:
Animation for earthquake terms and concepts
National Geographic
USGS Earthquake Hazards Program
Teaching Earthquake